The present invention relates generally to an apparatus and method for concentrically aligning parts. More specifically, it relates to an engine powered generator having a stator concentrically aligned with a rotor.
It is well known to power an electric generator using an engine. The flywheel of the engine is attached to the rotor of the generator. The rotor spins inside of a stator. The stator is held stationary inside of a housing. The stator housing assembly in turn is mounted to an adapter plate or fly wheel housing which is fixed to the engine behind the flywheel.
There is generally a small air gap between the rotor and the stator. The quality of the electric output of the generator is dependent upon the air gap having a constant size as the rotor spins. The rotor and the stator must be concentrically aligned with each other to achieve the desired constant size or dimensional uniformity.
Prior art attempts to achieve the required degree of concentricity involve tightly controlling the alignment of the stator housing assembly with the adapter plate. In one prior art method, the surface of the adapter plate is machined to form a circular pilot ring on its surface. The adaptor plate is fixedly mounted to the engine at a predetermined and known location behind the flywheel (which has the rotor attached to it). The stator is secured inside of the cylindrical housing, also at a predetermined and known location within the housing. The diameter of the end of the cylindrical stator housing assembly is slightly larger or slightly smaller than the diameter of the pilot ring on the adapter plate. The stator housing assembly, when placed over the rotor and aligned with the pilot ring, fits snugly onto the pilot ring. By tightly controlling the location and alignment of the stator housing assembly with respect to the pilot ring, therefore, the axis of the stator is indirectly forced into concentric alignment with the axis of the rotor.
This prior art method of alignment requires several expensive manufacturing steps to insure that the desired concentricity is obtained. For instance, the adaptor plate surface must be accurately machined to form and locate the pilot ring. This machining step is expensive. It is therefore desirable to have an adapter plate that does not require any machining.
One prior art housing is made from a relatively thin steel plate that is rolled into a cylinder and welded along the seam. A steel end ring is welded to each end of the housing to provide a proper surface for alignment with the continuous pilot ring. The end rings are made from relatively thick steel bar stock that is rolled into a ring and welded to the end of the housing. A gap is left between the ends of the rolled steel bar stock to accommodate the starter motor that extends out over the flywheel.
Different engine manufacturers locate the starter motor at different locations around the circumference of the flywheel. As a result, the location of the gap in the housing end ring that accommodates the starter motor is different for different engines and a different housing configuration must be provided for each different engine type. It is desirable therefore to have a single housing configuration that accommodates more than one type of engine.
The stator is press fit into the housing. A tight fit results when the stator contacts the inner surface of the housing at many points. The end rings are added to the housing assembly to provide a surface for alignment with the continuous pilot ring. These end rings add rigidity to the housing assembly and in the process may change the roundness of the housing. This results in the stator having too little contact to be securely held in place. It is necessary to drill through the housing into the stator and to weld the stator in place in these situations. The drilling process damages the painted outer surface of the housing and the housing must later be repainted to prevent corrosion from occurring. All of these additional steps to secure the stator in place add extra cost to the generator. It is therefore desirable to have a stator housing assembly without end rings wherein the stator is adequately secured in place by simply press fitting the stator into the housing without any further processing required.
The prior art cylindrical stator housing assembly also requires machining of the end rings to provide for proper and accurate alignment with the circular pilot ring. The stator housing assembly, which can weigh in excess of 200 pounds, is typically mounted on a lathe and the end rings are accurately machined thereon. This machining step is not only expensive, but in many cases dangerous due to the large weight of the spinning stator housing assembly on the lathe.
Another problem is that sharp metal chips produced during the machining operation can inadvertently land inside of the stator housing assembly. The stator is made up largely of copper wire that is insulated with, and sealed in, varnish. If left undetected, these stray metal chips can damage the insulation surrounding the copper wires. This can result in a shorted winding during operation of the generator. It is desirable therefore to entirely eliminate the machining operations applied to the stator assembly.
FIG. 1 shows a prior art generator 101 using a pilot ring to align the stator and rotor. Engine/rotor assembly 100 includes an engine (not shown), a flywheel 102, a starter motor (not shown), and a rotor 104. Rotor 104 is mounted to flywheel 102 at a predetermined and known location and spins with flywheel 102. The starter motor is used to start flywheel 102 spinning and typically protrudes outward from the side of flywheel 102. The location of the starter motor varies from engine manufacturer to engine manufacturer.
An adapter plate 105 is mounted to the engine block behind flywheel 102. Adapter plate 105 is also mounted at a predetermined and known location. Prior art adapter plate 105 includes a circular pilot ring 106 and mounting holes 107. Pilot ring 106 is created by machining the surface of adaptor plate 105, and has a mostly continuous outside pilot ring surface 109. Pilot ring 106 provides for alignment of a stator with rotor 104 as will be explained later.
A prior art stator housing assembly 200 is also shown in FIG. 1. Stator housing assembly 200 includes a stator 201 and a housing 202. Housing 202 typically is made by rolling a steel plate into a cylinder and then welding or otherwise joining the edges of the steel plate together. A steel end ring 203 is welded to each end of housing 202. Stator 201 is then press fit into housing 202. The location of stator 201 inside of housing 202 is also predetermined and known. One end of housing 202 is adapted for attachment to engine/rotor assembly 100. The other end of housing 202 is adapted for attachment to a bearing assembly or other device in a similar manner.
Steel end ring 203 is generally included to provide a surface on the end of stator housing assembly 200 that can be accurately machined. This insures that stator 201 will be concentrically aligned with rotor 104 when stator housing assembly 200 is attached to engine/rotor assembly 100. End ring 203 is typically formed from steel bar stock that is also rolled into shape. Unlike the steel plate used to make housing 202, however, the ends of the steel bar used to make end ring 203 are not brought together. Rather, the ends are left separated to form a starter motor gap (not shown) in end ring 203. The starter motor gap is located to accommodate the protruding starter motor when stator housing assembly 200 is mounted to engine/rotor assembly 100. Different engine manufacturers locate their starter motors at different locations around the flywheel. The starter motor gap must therefore be located at a different location for different engine types. Different stator housing assemblies are therefore needed for different engine types.
End ring 203 typically has a carefully machined inside end ring surface 205. End ring 203 also includes mounting holes 207, each of which is positioned to align with a corresponding mounting hole 107 on adapter plate 105.
Stator housing assembly 200 is mounted to engine/rotor assembly 100 in the following manner during assembly of the prior art welding generator. First, adapter plate 105, with a mostly continuous pilot ring 106 machined thereon, is mounted to the engine at a predetermined and known location behind flywheel 102. Next, stator housing assembly 200 (with stator 202 secured therein) is positioned in front of engine/rotor assembly 100 with the starter motor aligned with the starter motor gap in end ring 203. Stator housing assembly 200 is then brought into contact with engine/rotor assembly 100 as discussed below for various prior art embodiments.
Inside end ring surface 205 has a diameter that is slightly larger than the diameter of the mostly continuous outside pilot ring surface 109. The result is that end ring 203 tightly fits over and is in continuous contact with pilot ring 106. The tight fit between end ring 203 and pilot ring 106 insures that stator 201 will be concentrically aligned with rotor 104.
After final alignment stator housing assembly 200 is secured to engine/rotor assembly 100 at mounting holes 107 and corresponding mounting holes 207 (see FIG. 1) using bolts 108 or other fasteners.
A method (from a different art) of aligning a transmission with an engine is to use pins and pilot holes. Pins (usually two) are mounted on a plate on the engine, and pilot holes are drilled into the end face of the transmission (or flywheel housing). Each of the pins is located to be inserted into a corresponding pilot hole. The pilot holes must be accurately located to align with the pins and thereby provide the degree of concentricity needed. Accurately locating the holes with respect to the pins adds extra expense to the generator. It is desirable therefore to have a method for concentrically aligning the stator with the rotor that does not depend on accurate alignment of pins with pilot holes.
According to a first aspect of the invention an engine powered generator includes an engine and a plate mounted to the engine. A generator is mounted to the plate. The generator includes a rotor, a stator and a housing. The stator is secured in the housing. A plurality of pins on the plate contact a surface of the housing, to concentrically align the stator with the rotor.
According to a second aspect of the invention an engine powered generator includes an engine with a wall and an output shaft rotating about an axis. The wall has a plurality of pins located about the axis and protruding from the wall. A generator has a rotor, connected to the output shaft so that it and rotates about the axis, and a stator, secured in a housing. The housing has a housing surface. The generator is located on the wall by contacting the pins with the housing surface at a first end of the housing.
According to a third aspect of the invention a method for concentrically aligning a stator with a rotor of a generator includes mounting a first plate to the engine. The first plate has a plurality of pins on it. The stator is secured in a housing, and the housing is aligned with the plurality of pins such that each of the plurality of pins contacts a surface of the housing to concentrically align the stator with the rotor. The generator is mounted on the first plate.
The plurality of pins includes at least three pins, or at least six pins, and the pins are dowels and/or round in various alternative embodiments.
The plurality of pins contact an inner housing surface, or an outer housing surface in other alternatives, and the contact is tangential in other embodiments.
The housing has a circular cross section in one embodiment.
The wall is substantially normal to the axis, and the pins protrude from the wall parallel to the axis, and the stator is permanently affixed to the housing, in alternative embodiments.
Other principal features and advantages of the invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description and the appended claims.